Nowadays, the textile industry is experiencing a surge in the field of what is known as “functional” clothing. This clothing is made mainly of textile, natural, artificial or synthetic fibres comprising various active ingredients and enabling the clothing, for example, to store and give out heat, to release fragrances, moisturising and therapeutic agents fairly quickly, or even to trap or retain various organic or inorganic compounds coming into contact with the fibres, etc.
Generally, the active ingredients are encapsulated in microcapsules which are fixed to or associated with the fibres in various manners, for example by inclusion, coating, or even by ionic bonding. These microcapsules may be sensitive, for example, to body heat and/or to the external environment, thus influencing the release of different molecules.
With regard to the method of fixing by inclusion, the capsules are directly enclosed within the fibre. The advantage of this method is that the capsules are permanently fixed in the fibre. The drawback, however, is that this method can only be used for synthetic fibres threaded by extrusion at a low temperature. Also, the encapsulated active ingredient is not easily accessible or diffuses with difficulty through the membrane of the capsule and through the fibre to the surface thereof.
This is why, nowadays, coating technology is generally used to fix capsules onto any type of fibre, in particular onto natural fibres. The capsules are dispersed in a cross-linked polymer which is coated onto the fibres. In this case also, the capsules are permanently fixed and the method may be carried out without difficulty. However, the fibres thus coated with the cross-linked polymer in which the capsules are dispersed are not as pleasant to touch.
Furthermore, in the previous case, the encapsulated active ingredient is not easily accessible or has difficulty diffusing through the membrane of the capsule and through the varnish coating.
Another method also makes use of fixing the capsules, by ionic bonding, onto the fibres. This method utilises the fact that the fibres generally have surface potential. The capsules are synthesised so as to have cationic or anionic functional groups on the external surface of the membrane and are fixed by ionic bonding onto the fibres. In this case also, one advantage is that the method may be carried out in a very simple manner. The major drawback is the very resistance to wetting. After a few washes, almost all the capsules have disappeared from the surface of the fibres.
The latest techniques use the known methods for grafting dyes onto textile fibres, that is to say grafting by way of covalent bonding. Thus, for example, patent application WO 01/06054 discloses an active ingredient contained in a polymer capsule, of which the surface has reactive groups enabling said covalent bonding with the fibre via a binder.
However, the description of this technique is rather general and the examples relate only to cotton fibres, onto which capsules containing an active ingredient are grafted, said capsules being bonded to cotton fibres via a “bridge” formed by a resin having methylol groups.
In these examples, covalent bonding is created between two hydroxyl (—OH) groups with the elimination of a water molecule in the presence of a Lewis acid-type catalyst.
This method has many drawbacks, in particular that of producing water as a by-product and requiring use of a catalyst. Furthermore, the resin having methylol groups is a urea-type resin. These groups may inter-react in an undesirable manner with the polymer capsules, in particular by forming agglomerates of capsules detrimental to a good distribution of the capsules on the fibres.
The applicant has now discovered a method for grafting solid or hollow composite capsules onto fibres, in particular textile fibres, said method also being suitable for grafting said capsules onto any type of support, having directly or latently, or even after pretreatment, functional groups able to form covalent bonds with said capsules.